This application is a divisional application of pending U.S. patent application No. 13/945,937 field Jul. 19, 2013, assigned to Freescale Semiconductor, Inc.
The present invention relates generally to digital circuits and counters, and more particularly to a Gray code counter.
Counters are digital logic circuits used for counting occurrences of an event with respect to a clock signal. Examples of counters include asynchronous, synchronous, decade, and Gray code counters. Gray code counters are those in which any two successive counting states differ by only one bit. For example, a two-bit Gray code counter has the following counting states: 00→01→11→10, where any two successive states differ by just one-bit position.
A conventional n-bit Gray code counter has 2n counting states and uses ‘n’ flip-flops for generating these states. The flip-flops operate on a clock signal that is received at respective clock input terminals. The clock signal toggles at the clock input terminals even when the output of the corresponding flip-flop is not altered. This leads to a continuous charging and discharging at nodes internal to the flip-flops, which in turn leads to dynamic power dissipation.
Gray code counters are used extensively in digital logic design applications for sharing multi-bit count information between synchronous logic circuits that operate at different clock frequencies. Since conventional Gray code counter design is not modular by nature, complicated Karnaugh maps need to be solved to design a higher order Gray code counter (five bits or more) from a lower order Gray code counter. Solving higher order Karnaugh maps is a laborious task and leads to inefficiency during the design phase of a product. Additionally, the maximum operating frequency of conventional Gray code counters is limited by the size of the fan-in cone of the flip-flops, and operating the conventional Gray code counter at high frequencies leads to considerable dynamic power dissipation.
Therefore, it would be advantageous to have a Gray code counter that is modular, has low dynamic power dissipation, and can operate at high frequencies.